In recent years, an in-vehicle device having a navigation function is further provided with multiple functions, such as a tuning function of one-segment television broadcasting, in addition to a playback function of sound and image stored in CD or DVD. In general, such an in-vehicle device performs a multitasking operation to activate a navigation function, a playback and an indication function of sound and an image, and the like simultaneously. For example, JP-A-10-287188 and JPA-2005-199998 disclose multitasking operations for processing each of preset tasks within a specific time period, processing a task with high priority preferentially, and processing multiple tasks efficiently by utilizing a time-sharing operation.
Nevertheless, new functions are added to an in-vehicle device year by year. Consequently, an in-vehicle device is required to execute a large quantity of processings. In order to handle such a large quantity of processings quickly, modification of a hardware component, such as enhancement of processing speed of a processing unit such as a CPU and expansion of a memory device, is required for every model change of an in-vehicle device. Furthermore, processing load applied to a processing unit such as a CPU and a signal bus becomes significantly high in order to process various functions simultaneously. Consequently, processings are hardly completed within a predetermined time period. Thus, a task with a low priority may not be processed, and consequently malfunctions such as timeout and hang-up may occur.